Research & Reviews: Journal of Chemistry e-ISSN:2319-9849 p-ISSN:2322-00 Determination of Activation Energy of Saponification Reaction through pH Analysis Shin Ji Low* International School of Asia, Karuizawa (ISAK), Nagano Prefecture, Japan RESEARCH ARTICLE Received date: 21/12/2016 ABSTRACT Accepted date: 02/02/2017 Saponification is a chemical reaction that produces surfactants and Published date: 04/02/2017 glycerol from fatty acid triglycerides from lye and oil. This investigation is interested in determining the activation energy of the Saponification reaction *For Correspondence between the oleic acid triglyceride found in olive oil and sodium hydroxide solution. While the activation energy of the aforementioned reaction is Shin Ji Low, International School of Asia, theoretically known, current experimental values still deviate greatly. Since Karuizawa (ISAK), Nagano Prefecture, Japan, this investigation utilises a different method of rate determination, it is Tel: +60123825318. justied as a worthwhile investigation that may potentially provide a more accurate experimental value. E-mail: [email protected] This research paper explains the methodology of using a Venirez pH probe to measure the rate of the Saponification reaction. The pKw values Keywords: Saponification, pH Analysis, Activation have to also be taken into consideration due to the changing temperature energy sat which the experiment occurs. The pH values can then be used to measure the concentration of hydroxide ions which can then be used to and the rate constant which subsequently enables the determination of the activation energy. The determined value of the activation energy of this investigation is 2.76 J/mol which suggests that this method of determining the activation energy is valid. However, due to long reaction times, only two temperatures could be tested throughout this investigation which is reacted in a low condense in the reliability of this result. This investigation does however introduce a new method of determining the activation energy of Saponification reactions. The first draft of this paper was used as an extended essay for a higher level Chemistry course as part of an assignment. The publication of this research paper belongs solely to the Research and Reviews: Journal of Chemistry. INTRODUCTION Saponification Reaction Mechanism Determining the activation energy of the Saponification reaction will require a method of measurement of the rate of reaction. The rate of reaction will then allow the rate constant of the rate expression to be determined. The natural logarithm of the rate constant and the reciprocal of die rent temperatures will then be plotted to identify the activation energy. In order to identify a method of measurement, the Saponification reaction mechanism mistrust be understood. The Saponification reaction that is being investigated in this essay is primarily between the oleic-oleic-oleic triglyceride, 3C H5 (C18H33O2) and sodium hydroxide (NaOH). When both chemicals interact with each other, an exothermic hydrolysis equation occurs. The actual reagents used in this experiment will be olive oil and a 5 M sodium hydroxide aqueous solution therefore the other constituent compounds in olive oil have to also be considered. Based on the Second Edition of Olive Oil published by Science Direct, olive oil is composed of monounsaturated, poly unsaturated and saturated fatty acids: oleic, linoleic, palm tic and stearic acid respectively. However, approximately 99% of the olive oil is composed of triacylglycerol or triglycerides such that a very small RRJCHEM | Volume 6 | Issue 1 | March, 2017 1 Research & Reviews: Journal of Chemistry e-ISSN:2319-9849 p-ISSN:2322-00 portion of the olive oil contains free moving fatty acids and an array of lipids such as hydrocarbons, sterols, aliphatic alcohols, tocopherols, and pigments [2]. The main constituent compound in olive oil is typically the oleic-oleic-oleic triacylglycerol. The olive oil that was used for this investigation is Bosco Pure and Natural 100% Pure Olive Oil and the content of oleic acid is listed as 10 g for 14 g serving of olive oil. This approximates the oleic acid triglyceride to 70% of the total mass of olive. While side reactions between sodium hydroxide and the remaining triacylglycerol are will likely occurs, this investigation will focus solely on the reaction between the oleic-oleic- oleic triacylglycerol and the sodium hydroxide. C3H5(C18H33O2)3(l)+3 NaOH (aq) → C3H5(OH)3(l)+3 C7H33COONa(s) The chemical equation explains the reaction between the aqueous sodium hydroxide solution and the triglyceride to ultimately form the sodium oleate polyatomic ionic compound and glycerol. This reaction is known as the alkaline ester hydrolysis which forms sodium oleate which is soap and hence is also known as Saponification. This Saponification reaction includes the hydrolysis of the triacylglycerol by the sodium hydroxide by splits the ester into three oleate ions. The three hydroxide acts as the three hydroxyl groups that bond covalently to form glycerol. The three negative oleate ions bond ironically with the positive sodium ion to form the polyatomic ionic compound: sodium oleate. Understanding this alkaline hydrolysis reaction allows us to determine a method of measuring the rate of reaction as it can be inferred that the pH at the beginning and the end of the experiment differs. This is because more and more of the hydroxide ions will be become the hydroxyl group of the glycerol and no longer free moving. Even though the sodium oleate is still alkaline, the rate of reaction can then be determined by calculating the change in pH. The change in pH can then be converted into the change in concentration of hydroxide ions. More information about how this method of rate determination was developed can be found further. Measuring rate of reaction is an interesting note is that the hydrophobic and hydrophilic ends of the sodium oleate compound allows it make water and oil miscible. Calculating the Rate of Reaction based on pH Values Determining the activation energy of a reaction typically requires the plotting of the Arrhenius equation in the natural log form. Calculating the rate of reaction for this particular reaction cannot be done through a change in mass or volume of gas emitted but can be determined by the change of concentration of sodium hydroxide solution. Baghdad University carried out a similar experiment to identify the kinetics of the Saponification reaction by taking samples every 5 to 10 min which is then titrated against hydrochloric acid to determine the remaining concentration of sodium hydroxide. However, I personally thought measuring the change in pH using Vernier pH probes would prevent doing many titrations. The pH value throughout the experiment can be measured and can then be converted to pH to then nd out the concentration of hydroxide ions. The decrease in the pH value reacts in a decrease in free moving hydroxide ions. It can then be inferred that the decrease in hydroxide ions is also equal to the rate of formation of sodium oleate as the mole ratio between the two compounds is 1:1 based on the chemical equation. However, since the temperature will be varied, the change in the water ionization constant, or Kw, of the water at different temperatures has to be considered when converting the pH value into the pOH value. Since the pH value is simply a function of calculating the concentration of free moving hydrogen or hydroxide ions, it is erected by the factors erecting the equilibrium constant. As the temperature increases, the equilibrium constant shifts toward the left side of reaction and the net concentration of hydroxide ions decreases. Therefore, the pH calculated based on the pH has to take the Kw of the water at different temperatures into consideration and it cannot be assumed that water is at pH 7. The European Physical Journal D has a list of water ionisation constants at different temperatures that can be used to calculate the pH values [1]. The following equation will then be used to determine the pOH value: pOH=pKw-pH Once the pOH value is determined throughout the reaction time, the average rate of reaction can then be determined (Table 1). Order of Saponification Reaction It can be inferred based on the literature obtained from Dr. Raghdads results in his published paper in the Journal of Engineering that the order of reaction between olefin, otherwise known as the oleic acid triglyceride, and sodium hydroxide is 2 (150). The discussion of his results revealed that the order with respect to olein and sodium hydroxide are both 1 respectively. The results of his experiments that explain the order of the reaction will be used as the basis of calculating the rate constant for this investigation. The following equation will be used to calculate the rate constant, k. k = Rate of Reaction/[NaOH][C_3H_5(C_18H_33O_2)_3] A literature value for the rate constant will be used as the procedure to create different concentrations of olein is not defined. RRJCHEM | Volume 6 | Issue 1 | March, 2017 2 Research & Reviews: Journal of Chemistry e-ISSN:2319-9849 p-ISSN:2322-00 Since it is an organic compound, the olive oil used is insoluble in water and dissolving it in different organic compounds might risk unwanted side reactions. The natural logarithm of the rate constant can then be plotted against the reciprocal of temperature in order to and the activation energy as well as the Arrhenius constant. DEVELOPMENT OF METHOD The method is loosely based of Dr. Raghads procedure but uses a change in pH instead of several titrations in order to measure the rate of reaction (149). Measuring Temperature The initial experimental setup used a magnetic heating stirrer to initially heat up the sodium hydroxide solution before adding the olive oil. A mercury thermometer was then used in order to monitor the temperature of the mixture.